To use HALT to its best advantage, take a systematic approach to root cause analysis, proceeding from the least destructive to most destructive methodology until root causes are conclusively identified and the failure mode, site and mechanism are categorized. Here’s how:

Information Gathering

The crucial first step in any failure analysis effort, information gathering needs to be done in an organized way, using standard nomenclature.

Crucial failure data to collect revolves around:

Failure history: when the failure occurred; the stresses being applied to determine possible failure location; and, any changes the device being tested underwent

Failure mode: the failure behavior experienced by the observer

Failure site: the presumed location of the failure

Failure mechanism: the factor causing the failure (like vibration or temperature cycling), not considered a root cause

Non-Destructive Evaluation Methods

Non-Destructive Evaluation (NDE) is designed to provide maximum information with minimal risk of damaging or destroying physical evidence.

A broad range of NDE methods are available, including:

Electrical Characterization is considered the most critical step in failure analysis, especially for failures induced during temperature step stress testing. Electrical characterization is the only way to determine recoverable failures (operational limits) and permanent failures (destruct limits). There are a number of common electrical characterization techniques:

LCR Meter: Measures inductance, capacitance and resistance of electronic components; in simpler versions, impedance is measured internally and converted for display to the corresponding capacitance or inductance value

Visual Inspection is exactly as the name implies – the product is observed in its physical state to detect defects.

X-ray Microscopy has the greatest potential for finding solder joint failures under area array devices. It detects voiding or poor wetting, providing evidence of root cause failures during the application of cyclic stresses. A major detractor, however, is difficulty related to identifying micro-cracks that occur during solder fatigue or fracture.

Thermal Imaging is best used when individual components fail, especially when there is elevated current leakage. Although rarely used, the process can provide evidence of excessive temperature rise and identify root cause of failures occurring at temperatures below expectations.

Superconducting Quantum Interference Device (SQUID) Microscopy uses a highly sensitive magnetic detector to find faults in circuits. SQUID requires that the device being tested is a flat shape, and is often preferred to thermal testing because it causes very little damage.

Acoustic Microscopy uses high or ultra high frequency ultrasound to penetrate solid materials and reveal visible images of internal defects like cracks, delaminations and voids.

Destructive Evaluation Methods

Destructive Evaluation (DE) is used when information obtained during NDE is insufficient to conclusively identify the root cause of failure.

DE primarily consists of two techniques:

Cross Sectioning identifies the failure site and removes a sample using band saws with diamond-encrusted blades to minimize damage to the printed circuit board assembly (PCBA). The sample is epoxy-mounted near the plane of interest to prevent relative movement and improve handling during grinding and polishing, which is done to reveal microstructural elements.

Sherlock Automated Design Analysis™ Software

Sherlock Automated Design Analysis™ software can be used to asses the validity of the failure mechanisms and provide mode shapes and stresses predictions during vibration, provided the vibration loads were sufficient to fail the interconnect and the defects were identified during failure analysis. If not, there may be an issue with the testing procedure.

Combining Sherlock with HALT root cause analysis can be powerful. Contact us today if you are interested in learning more, or check out our Common Mistakes by Electronic Design Teams webinar by clicking the link below.